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WASHINGTON -- People are inventing so many new, legal ways to get high that lawmakers can't seem to keep up.

MORE: Bath salts still emerging on the First Coast

Over the past two years, the U.S. has seen a surge in the use of synthetic drugs made of legal chemicals that mimic the effects of illegal stimulants.

The drugs are often sold at independent stores in misleading packaging that suggests common household items like bath salts and plant food. But the substances inside are mind-altering drugs that have been linked to violent behavior.

President Barack Obama signed a bill into law earlier this month that bans the sale, production and possession of more than two dozen of the most common bath salt drugs. But health professionals say that there are so many different varieties that lawmakers are playing catch up.